entities in mathematics There is a line of argument which keeps ontological commitments to the minimum by making use of conservativity results. The argument goes back to Hilbert who set its general frame. Hilbert’s concern was with certain abstract (ideal) entities in mathematics but the argument has been applied without discrimination to avoid ontological commitment to mathematical entities in physics (Field) or to avoid an ontological commitment to substantial properties in the case of truth (Horwich, Field, Williams).